1. Field of the Invention
The invention relates to hybrid electric vehicles of the type including an internal combustion engine, a traction battery, and a hybrid electric powertrain. The invention further relates to controlling the powertrain such that battery power remains within the battery charge and discharge limits.
2. Background Art
In an existing hybrid electric vehicle, a hybrid electric vehicle powertrain includes a vehicle system controller (VSC), an internal combustion engine, a traction battery, and a transmission including a motor-generator subsystem. These components form a powersplit powertrain, and the VSC may control the components in an attempt to maximize fuel economy.
It is possible that, under some circumstances, the traction battery power may fall below a battery power charge limit or exceed a battery power discharge limit.
Background information may be found in U.S. Pat. No. 7,295,902 and U.S. Pub. No. 2005/0003927.
Further background information may be found in SAE Paper No. 2006-01-3571, October 2006, Liang Chu, Jilin University. Abstract: The new control algorithm for parallel hybrid electric vehicle is presented systematically, in which engine operation points are limited within higher efficient area by the control algorithm and the state of charge (SOC) is limited in a range in order to enhance the batteries' charging and discharging efficiency. In order to determine the ideal operating point of the vehicle's engine, the control strategy uses a lookup table to determine the torque output of the engine. The off-line simulation model of parallel HEV powertrain is developed which includes the control system and controlled objective (such as engine, electric motor, battery pack and so on). The results show that the control algorithm can effectively limit engine and battery operation points and much more fuel economy can be achieved than that of conventional one.